Field of the Invention
The present invention relates to a DC-DC converter and, more specifically, to a DC-DC converter that is operational in a high-power mode of operation and a low-power mode of operation.
Description of Related Art
In vehicles, such as automated people movers, a vehicle can include wheels which are configured to travel along a path. These wheels can be tired wheels or, where the path includes rails, the wheels can be conventional rail wheels designed to travel on said rails. In such people movers, it is desired that HVAC systems of such vehicles be operational for 30 minutes or more from battery energy after a grid power failure. To accomplish this, a DC-DC converter typically used to convert high voltage provided on the power grid, for example 750 volts DC, to a lower voltage, for example 100 volts DC, that can be utilized with internal systems within the vehicle, such as overhead lighting, control systems, and the like.
In a normal mode of operation, the converter works in a step-down mode to charge and maintain the voltage of a low voltage DC battery, e.g., a 100 volt DC battery, from the high voltage, e.g., 750 volts DC, available via the power grid.
In an emergency mode, it would be desirable to have the DC-DC converter work in a step-up mode to boost the low voltage (110 VDC) to a high voltage (750 VDC) to feed the HVAC system.
In another example, it would be desirable to enable a vehicle to move to or from a maintenance facility utilizing electrical energy stored in the low voltage battery. For this again, the DC-DC converter is desirably operated in a step-up mode to convert low voltage energy (110 VDC) to high voltage energy (750 VDC) to feed the propulsion system.
Using the DC-DC converter in step-up mode is a high-power operation. Accordingly, it is desired to have high conversion efficiency in step-up operation so as not to waste valuable energy. In contrast, the step-down operation can be high power (when the battery is empty and must be recharged rapidly) or low power (when the battery is less than fully charged).
Heretofore, standard single-mode bidirectional converters have lower efficiency at low power operation, which is most of the time. Accordingly, it would be desirable to enhance the low power efficiency of a bidirectional DC-DC converter with no added active or passive components and with no modification in high power operation and at no additional cost.